1. Field of the Invention
This invention relates to novel photoresist compositions for forming positive resist images on a surface and to device fabrication using such novel compositions. The instant composition contains polymers having Pendant acid labile groups in the presence of acid generators comprising novel diazonium salts.
2. Art Background
Lithographic patterning of circuit components has become useful in the field of device fabrication, e.g., semiconductor device fabrication, interconnection media such as printed circuit boards, and optoelectronic device fabrication. (See, for example, C. Grant Willson and Murrae J. Bowden, "Resist Materials For Microelectronics," ChemTech, pages 102-111 (Feb. 1989.) Such processes involve the fabrication of devices or patterned regions on a substrate such as a semiconductor substrate, e.g., silicon or on a chromium coated mask substrate. (Substrate in the context of this invention refers to the wafer, board or mask on which the device or pattern is being formed and includes in the former case, if present, regions of semiconductor material, dielectric material, and electrically conducting material or in the latter case, optically transmitting material.) The fabrication procedure generally requires at least one step in which a resist material is formed on the substrate and a pattern is delineated in this material by exposure to correspondingly patterned, actinic radiation, e.g., deep ultraviolet radiarion (150 to 300 nanometers), x-radiation (0.4 to 10 nanometers), ultraviolet radiation (300 to 400 nanometers), visible radiation (400 to 700 nanometers) and particle beams such as ion and electron beams. The actinic radiation produces a chemical reaction in the film which in turn introduces a difference in solubility between the exposed and unexposed regions The exposed pattern in the resist is developed with a suitable solvent that preferentially solubilizes the exposed or unexposed region. The pattern thus produced in the resist material is employed as a protective barrier in subsequent device fabrication steps such as etching, ion implantation, deposition and dopant diffusion or employed as a protective barrier for etching mask substrates.
Various resist materials relying on a wide variety of chemistries have been proposed for use in device fabrication. One such approach is discussed in U.S. Pat. No. 3,779,778. This approach employs a water insoluble polymer containing one or more acid degradable groups and a photosensitive acid generator. Examples of photoacid generating compounds are described in a paper by J. V. Crivello, "The Chemistry of Photoacid Generating Compounds" in Polymeric Materials Science and Engineering Preprints, Vol. 61, Amer. Chem. Soc. Meeting, Miami, Fla., Sept. 11-15, 1989, pp. 62-66 and references therein. The crux of this approach involves the use of a radiolytic acid generator and a polymer whose pendant groups are chosen to be catalytically acid labile; thus, the polymer is disclosed to contain one or more acid degradable linkages which are formed by the nucleophilic reaction of hydroxy aromatic compounds, N-alkylaryl sulfonamides or certain secondary amines with alkyl vinyl ether such as methyl vinyl ether, ethyl vinyl ether or dihydropyran. (As to this last embodiment, the reactions of dihydropyran materials as protecting groups removed by relatively mild conditions are described by J. E. Kerns et al., Journal of Macromolecular Science and Chemistry, A8(4), 673 (1974)). (See also Canadian Pat. No. 672,947).
U.S. Pat. No. 4,491,628 also discloses resist materials sensitive to ultraviolet, deep ultraviolet, electron beam and x-ray radiation employing an acid generator with a polymer having acid labile pendant groups. The polymers include recurrent pendant groups such as tertiary butyl ester or tertiary butyl carbonate groups together with a generator of acid that catalytically converts the protecting moiety to an aqueous base solubilizing group. (A sensitizer that alters wavelength sensitivity also is discussed.) The preferred acid labile pendant groups are tertiary butyl esters of carboxylic acids and tertiary butyl ethers and carbonates of phenols. However, other acid labile groups such as trityl, benzyl, benzylhydryl as well as others characterized as "well known in the art" are discussed.
In a third resist employing an acid generator and polymer combination (European Patent Application 0264908) the auto decomposition temperature of the polymer, copolymer or terpolymer employed is increased to greater than 160.degree. C. by employing pendant groups that form secondary carbonium ion intermediates with an available adjacent proton.
In other approaches to resist chemistries, a polymer (without radiation sensitive acid generator) is formulated to have a backbone and pendant group that together yield the desired properties. Such material described in Japanese Kokai No. SH057 [1983] 118641 includes a methyl methacrylate backbone and alkoxyalkyl pendant groups. Presently a desirable formulation goal for any photoresist is a sensitivity better than 30 mJ/CM.sup.2 for utility in the deep ultraviolet range, and better than 10 .mu.C/cm.sup.2 for use with electron radiation, with a resolution better than 1.0 .mu.m.
Co-pending Ser. No. 07/388,404 filed on Aug. 2, 1989 discloses thermally stable carbazole diazonium salts and is incorporated herein in its entirety.